Aligned carbon nanotubes

ABSTRACT

Methods of forming carbon nanotubes and structures and devices including carbon nanotubes are disclosed. Methods of forming the carbon nanotubes include patterning a surface of a substrate with polymeric material, removing portions of the polymeric material to form exposed substrate surface sections, and forming the carbon nanotubes on the exposed substrate sections.

FIELD OF INVENTION

The present disclosure generally relates to methods for forming carbon nanotubes. More particularly, the disclosure relates to methods suitable for forming carbon nanotubes and to structures and devices including carbon nanotubes.

BACKGROUND OF THE DISCLOSURE

Carbon nanotubes have several desirable properties, including high thermal conductivity, high mechanical strength and hardness, and excellent conducting or semiconducting properties. Accordingly, carbon nanotubes can be beneficially used in a wide variety of applications. For example, carbon nanotubes can be used in the manufacture of electrical energy storage devices (e.g., as a spring or a battery component), for microelectronic devices (e.g., transistors, non-volatile memory, photonic devices, and the like), for medical devices or systems (e.g., bio sensors, drug delivery systems, and tissue engineering), as protective coatings, and many others to provide desired performance of such devices or systems.

Carbon nanotubes can be formed using several different techniques, including laser ablation, arc discharge, electrolysis, and chemical vapor deposition (CVD). Of these various techniques, CVD is generally thought to be the most suitable for high-volume manufacturing of carbon nanotubes.

CVD carbon nanotube formation techniques generally use a metal nanoparticle catalyst on a surface of a substrate. The diameter of the nanotubes and properties of the nanotubes generally correspond to the type and size of the metal catalyst nanoparticle on the substrate surface. Unfortunately, location and size of the metal catalyst nanoparticles are difficult to control. As a result, the growth location and direction, size, chirality, and properties (e.g., band gap) of carbon nanotubes formed using these techniques are also difficult to control.

One technique that has been proposed for forming aligned carbon nanotubes includes electron beam induced deposition of nanoparticle metal catalyst material onto a substrate surface. It is thought that electron beam induced deposition will be able to control the location and size of the deposited catalyst onto the substrate surface. However, such techniques are relatedly slow and expensive and thus are not well suited for high-volume manufacturing.

Crystalline substrates, such as quartz substrates, have been used to form aligned carbon nanotubes, offering some control of the size and chirality of the carbon nanotubes formed using the quartz substrates. However, carbon nanotubes formed using such techniques generally require transfer to another substrate—e.g., a device suitable substrate that includes various layers used to form a device. As a result, the techniques are also not generally suitable for high-volume manufacturing of devices that include carbon nanotubes.

Accordingly, improved methods of forming aligned carbon nanotubes, including methods suitable for high-volume manufacturing, and structures and devices including carbon nanotubes, are desired.

SUMMARY OF THE DISCLOSURE

The present disclosure generally relates to methods of forming carbon nanotubes on a surface of a substrate and to structures and devices including carbon nanotubes. Exemplary methods of forming carbon nanotubes can be used to form aligned carbon nanotubes on substrates that are suitable for device manufacturing; thereby, not requiring transferring of the carbon nanotubes from one substrate to another to form devices including the carbon nanotubes. The methods can also be used to form aligned carbon nanotubes having desired sizes and/or size distributions on the substrate surface.

As set forth in more detail below, exemplary methods of forming carbon nanotubes use patterned polymeric material to form sections on a substrate on which aligned catalyst features or particles can be formed. The aligned catalyst features or particles, in turn, can be used to form an aligned pattern of carbon nanotubes on the substrate sections.

In accordance with various embodiments of the disclosure, methods of forming carbon nanotubes include providing a substrate having a surface, disposing a polymeric material onto the surface, patterning the polymeric material, removing portions of the polymeric material to form exposed sections on the surface, and forming carbon nanotubes on the sections. The methods can include the use of directed self-assembly polymeric material, which allows for the formation of features having small dimensions of, for example, less than 100 nm, less than 50 nm, less than 30 nm, less than 20 nm, less than 10 nm or less than 5 nm. The methods can also include a step of forming catalyst material (e.g., material including one or more of Co, Ni, Fe, Mo, or the like) on the sections of the exposed substrate. By way of examples, the step of forming catalyst material includes selective decomposition of one or more organometallic precursors comprising the catalyst material, allowing selective formation of the catalyst material (e.g., nanoparticles) on the exposed sections of the substrate. Initially deposited catalyst material can be heated or annealed to transform the initially deposited catalyst material to islands (features) or nanoparticles of the catalyst material on the sections; these islands or nanoparticles serve as a catalyst for carbon nanotube formation. The methods can additionally include a step of forming patterned features (e.g., metal features) onto the substrate surface to facilitate alignment of polymeric features (e.g., lines) formed during the step of patterning. The catalyst material can be formed overlying the (e.g., exposed) substrate surface using chemical vapor deposition (CVD) processing, e.g., selective decomposition of a catalyst-containing precursor. The CVD process can include cyclic CVD deposition processing (e.g., atomic layer deposition (ALD) processing). Similarly, the carbon nanotubes can be formed using CVD processing.

In accordance with further exemplary embodiments of the disclosure, structures include one or more carbon nanotubes—e.g., one or more carbon nanotubes formed according to a method described herein. Exemplary structures include a substrate (e.g., having an insulating layer formed on a surface), catalyst material formed overlying the substrate surface, and carbon nanotubes formed overlying the catalyst material. The catalyst material can be in the form of nanostructures, nanoparticles, continuous film, or semi-continuous film.

In accordance with further exemplary embodiments of the disclosure, a device includes a structure, such as a structure described herein, and additional layers and/or materials used to make devices. For example, the device can include additional conducting (e.g., metal), insulating, dielectric, and/or semiconductive layers.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 illustrates a method of forming carbon nanotubes in accordance with exemplary embodiments of the disclosure.

FIG. 2 illustrates a substrate on which carbon nanotubes can be formed.

FIG. 3 illustrates a structure including patterned features.

FIG. 4 illustrates a structure including polymeric material disposed on a substrate surface in accordance with exemplary embodiments of the disclosure.

FIG. 5 illustrates a structure including aligned polymeric features in accordance with exemplary embodiments of the disclosure.

FIG. 6 illustrates a structure having a portion of the aligned polymeric features removed in accordance with exemplary embodiments of the disclosure.

FIG. 7 illustrates a structure having catalyst material deposited between polymeric features and onto sections of a substrate surface in accordance with exemplary embodiments of the disclosure.

FIG. 8 illustrates a structure having catalyst material deposited onto sections of a substrate surface in accordance with exemplary embodiments of the disclosure.

FIG. 9 illustrates a structure including catalyst nanoparticles formed on a substrate surface in accordance with exemplary embodiments of the disclosure.

FIG. 10 illustrates a structure including aligned carbon nanotubes formed overlying a substrate surface in accordance with exemplary embodiments of the disclosure.

FIG. 11 illustrates a device including a carbon nanotube in accordance with yet additional exemplary embodiments of the disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE DISCLOSURE

The description of methods, structures, and devices provided below is merely exemplary and is intended for purposes of illustration only; the following description is not intended to limit the scope of the disclosure or the claims. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features.

The present disclosure generally relates to methods of forming carbon nanotubes and to structures and devices including carbon nanotubes. As set forth in more detail below, carbon nanotubes formed in accordance with various examples of the present disclosure can be used for a wide variety of applications, including, but not limited to, electrical energy storage, microelectronic applications, medical applications, protective coatings, and many other applications. Further, exemplary methods are relatively easy and inexpensive, can be used to form the carbon nanotubes in a time-efficient manner, can be used to form carbon nanotubes on insulating and/or amorphous surfaces, and/or are suitable for high-volume manufacturing.

Turning now to the figures, FIG. 1 illustrates a method 100 of forming carbon nanotubes in accordance with various exemplary embodiments of the disclosure and FIGS. 2-10 illustrate structures formed according to the steps of method 100. Method 100 includes the steps of providing a substrate (step 102), disposing polymeric material onto a surface of the substrate (step 104), patterning the polymeric material (step 106), removing portions of the polymeric material to form exposed sections on the substrate surface (step 108), forming catalyst material on the exposed sections (step 110), removing any excess or remaining polymeric material (step 112), forming carbon nanotubes using the catalyst material (step 114), and optionally forming patterned features on a substrate surface (step 116).

During step 102, one or more substrates (e.g., a substrate 202, illustrated in FIG. 2) are provided. Substrate 202 can include any material having a surface onto which carbon nanotubes can be formed. Substrate 202 can include a bulk material such as silicon (e.g., single crystal silicon), a sacrificial substrate, such as a ceramic or a polymer, and may include one or more layers overlying bulk material. Further, substrate 202 can include various features, such as trenches, vias, lines, and the like formed within or on at least a portion of the substrate. The features can have an aspect ratio, defined as a feature's height divided by the feature's width, of, for example, greater than or equal to 5, greater than or equal to 10, greater than or equal to 15, or greater than or equal to 20. By way of examples, substrate 202 includes materials, such as layers of insulating and conducting materials, suitable for forming a device including one or more carbon nanotubes. In these cases, a surface 204 of substrate 202 can include insulating material, such as silicon oxide (SiO_(x)), or other insulating or dielectric materials.

At step 104, polymeric material 402 is disposed onto surface 204 of substrate 202. The polymeric material can be disposed by depositing the polymeric material onto surface 204 using any suitable means, such as spin-on coating techniques. Exemplary polymeric materials suitable for use in step 104 include polymers that can be patterned such that portions of the polymeric material can be selectively removed. Photoresist materials are suitable for use as polymeric material 402. Additional suitable polymeric materials include directed self-assembly polymeric materials, such as block copolymers, which are molecules composed of two or more polymers connected to each other via covalent bonds. By way of examples, polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), which includes polystyrene (PS) and poly(methyl methacrylate) (PMMA) polymers that are covalently linked, is a suitable polymeric material 402 for use in step 104. Another suitable block copolymer includes polystyrene-b-polyisoprene-b-polystyrene (PS-b-PI-b-PS). In the case of block copolymers, the polymers or blocks can phase separate and form aligned structures with ordered nanoscale domains (e.g., less than 100 nm dimension(s)) in various configurations such as spheres, cylinders, or lines. The characteristic shape and dimensions of these domains can be tuned via polymeric design.

With reference to optional step 116 and FIG. 3, patterned features 302, 304 can be formed on surface 204 of substrate 202 to facilitate alignment and/or desired configuration of the phase-separated domains. Patterned features 302, 304 can be formed of any suitable material, and can be formed using deposition and etch or other suitable techniques. For example, a layer of metal, such as Co or Ni, can be deposited onto surface 204 and the metal can be patterned and etched to form features 302, 304 having a pitch of less than about 500 nm, less than about 200 nm, less than about 100 nm, less than about 75 nm, less than about 50 nm or less than about 30 nm. The phase-separated domains (e.g., first domains 502 and second domains 504, illustrated in FIG. 5) of polymeric material 402 can be used to reduce a pitch of sections of surface 204 that are available for subsequent formation of catalyst material and/or carbon nanotubes.

During step 106, the polymeric material is patterned. As noted above, in the case of phase-separable material, the polymeric material can be patterned using features 302, 304 to facilitate alignment of phases of the polymeric material and phase separating the polymeric material (e.g., a block copolymer) into aligned first domains 502 and second domains 504, as illustrated in FIG. 5. An annealing process can be used to separate the phases of the polymeric material. The annealing process can include, for example, heating a structure to a temperature of about 50° C. to about 400° C., about 100° C. to about 350° C., about 150° C. to about 300° C., about 175° C. to about 300° C. or about 200° C. to about 275° C. in the presence of a gas atmosphere, such as inert gas atmosphere like N₂ or noble gas atmosphere like Ar or He. In some instances the annealing atmosphere can also comprises hydrogen, such as H₂ or mixtures of H₂ and N₂, or oxygen such as O₂, or mixtures comprising any gases mentioned above. Depending on the polymeric material, the annealing temperature might vary. Although illustrated with two separate domains or phases, polymers that can be separated into more domains can also be used in accordance with this disclosure.

Once the polymeric material is patterned, portions of polymeric material 402 (e.g., first sections 502 or second sections 504) can be selectively removed during step 108 to form a substrate surface having patterned polymeric material thereon (e.g., patterned polymeric features on the substrate surface). By way of example, when polymeric material 402 includes PS-b-PMMA, the PMMA blocks (e.g., second sections 504) can be selectively removed, leaving exposed substrate sections 602. The portions can be removed using a solvent or etchant, such as oxygen based etching, for example O₂ based, reactive ion etching (ME) or O₃ or using excited species of an oxygen-containing compound (e.g., oxygen cations, oxygen anions, oxygen radicals), which can be formed using an in-situ (or direct) or remote plasma (or radical) generator. When polymeric material 402 is separated into three or more phases, one, two, or more phases of the polymeric material can be selectively removed. To further enhance selectivity of removal rates of first sections 502 and second sections 504, polymeric material 402 can be treated with a modifier, such as a modifier disclosed in U.S. Pat. No. 8,980,418, entitled SEQUENTIAL INFILTRATION SYNTHESIS FOR ADVANCED LITHOGRAPHY, issued Mar. 17, 2015, the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure. FIG. 6 illustrates a structure including exposed substrate surface sections 602 that are formed once portions of polymeric material 402 are removed.

In accordance with various illustrative embodiments, once the structure including exposed substrate surface sections is formed, the substrate, including patterned polymeric material, can be introduced to a reaction space, such as a reaction space of a CVD, ALD, or cyclic deposition reactor, to form catalyst material and/or carbon nanotubes on the exposed substrate surface sections.

During step 110, catalyst material can be formed on exposed substrate surface sections 602. For example, catalyst material 702 can be formed on exposed substrate surface sections 602 using selective decomposition of one or more metal-containing precursors (e.g., an organometallic precursor) including catalyst material. The metal precursor can comprise one or more metals selected from the group consisting of Bi, Mg, Ca, Sr, Rb, Cs, Ba, Ni, Mn, Cu, Co, Ti, Ta, Zr, Hf, V, Nb, Cr, W, Mo, Sc, Y, Lu, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Fe, Zn, Sn, Sb, Cr, In, Cd, Ga, Ge, B, As, Al, Si, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au, Hg, and Pb. For example, the metal precursor (and hence the catalyst material) can include one or more metals selected from the group consisting of Cr, Cu, Ni, Fe, Co, Zn, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Mo and W. The catalyst can include one or more noble metals.

Preferred metal precursors include cyclopentadienyl and betadiketonate metal compounds, more preferably metallocene compounds, beta-diketonate compounds and acetamidinato compounds. Particularly preferred metal precursors are cyclopentadienyl and acetylacetonate (acac) precursor compounds. In some embodiments, a bis(ethylcyclopentadienyl) metal compound is used.

When depositing ruthenium thin films or particles, preferred metal precursors may be selected from the group consisting of bis(cyclopentadienyl)ruthenium, tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium, 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl) ruthenium, and tris(N,N′-diisopropylacetamidinato)ruthenium(III) and their derivatives, such as bis(N,N′-diisopropylacetamidinato)ruthenium(II) dicarbonyl, bis(ethylcyclopentadienyl) ruthenium, bis(pentamethylcyclopentadienyl)ruthenium and bis(2,2,6,6-tetramethyl-3,5-heptanedionato)(1,5-cyclooctadiene)ruthenium(II). In preferred embodiments, the precursor is bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2), bis(2,4-dimethylpentadienyl)ruthenium or (2,4-dimethylpentadienyl)(ethylcyclopentadienyl)ruthenium.

When depositing platinum films or particles, preferred metal precursors include (trimethyl)methylcyclopentadienylplatinum, platinum (II) acetylacetonato, bis(2,2,6,6-tetramethyl-3,5-heptanedionato)platinum(II) and their derivatives.

When depositing iridium films or particles, preferred metal precursors include tris(acetylacetonato)iridium(III) and derivatives of those.

When depositing palladium films or particles, preferred metal precursors include bis(hexafluoroacetylacetonate)palladium(II).

When depositing nickel-containing films or particles, preferred metal precursors include nickel chloride, bis(acetylacetonate)nickel(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II) and bis(cyclopentadienyl)nickel(II) and derivatives of those.

When depositing cobalt-containing films or particles, preferred metal precursors include bis(acetylacetonate)cobalt(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(II) and bis(cyclopentadienyl)cobalt(II) and derivatives of those.

When depositing cobalt-containing films or particles, preferred metal precursors include bis(acetylacetonate)cobalt(II), bis(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(II), tris(acetylacetonate)cobalt(III), tris(2,2,6,6-tetramethyl-3,5-heptanedionato)cobalt(III) and bis(cyclopentadienyl)cobalt(II) and derivatives of those.

When depositing copper-containing films or particles, preferred metal precursors include copper chloride, bis(acetylacetonate)copper(II) and bis(2,2,6,6-tetramethyl-3,5-heptanedionato)copper(II) and derivatives of those.

When depositing chromium-containing films or particles, preferred metal precursors include tris(acetylacetonate)chromium(III) and derivatives of those.

When depositing iron-containing films or particles, preferred metal precursors include acetylacetonate compounds of iron and ferrocene compounds and derivatives of those.

When depositing zinc-containing films or particles, preferred metal precursors include alkylzinc compounds, such as diethylzinc(II).

When depositing tungsten or molybdenum-containing films or particles, preferred metal precursors include metalorganic compounds, such as cyclopentadienyl-, alkylamide- and imido-amino-compounds of tungsten and molybdenum.

The catalyst material can be deposited as a film on exposed substrate surface sections 602. The deposited films can be continuous or non-continuous—e.g., form islands of metal at distinct sites on the surface, while other sites do not contain metal. The islands can be three-dimensional structures and include metal “particles” or “grains.” The catalyst material—e.g., metal particles—serve as nucleation points for carbon nanotube growth. As discussed in more detail below, the deposited film can be treated to form particles, such as nanoparticles that are used for the carbon nanotube growth.

In accordance with various embodiments of the disclosure, a cyclic deposition process is used to form or deposit catalyst material onto substrate surface 204. In these cases, vapor or gas phase reactants are separately provided to a reaction space of a reaction chamber, for example, by removing or purging excess reactants and/or reactant byproducts from the reaction chamber between reactant pulses. This purge step may be accomplished with an evacuation step and/or with the aid of an inactive gas pulse. In some embodiments, an inactive carrier gas is used to feed the reactants into the reaction chamber and also serves as a purge gas to push excess reactants and/or reaction byproducts out of the reaction chamber.

A cyclic deposition process (e.g., but not restricted to, an atomic layer deposition (ALD) process) includes alternating and sequential provision (or pulses) of a first and second reactant to a reaction space, such as a reaction chamber. Depending on the nature of the film to be formed, additional reactants may be included. The first reactant is conducted into the reaction space in the form of gas phase pulse, optionally with the aid of a carrier gas, and contacted with the surface of the substrate (e.g., exposed substrate surface sections 602). Conditions can be selected such that no more than about one monolayer of the precursor is adsorbed on the substrate surface in a self-limiting manner per cycle. Excess first reactant and reaction byproducts, if any, are purged from the reaction chamber, often with a pulse of inert gas such as nitrogen or argon. This can be accomplished, for example, by turning off the flow of reactant to an inert carrier gas, while continuing to flow the carrier gas through the chamber.

In the case of cyclic deposition, the first reactant can include any of the metal-containing precursor(s) noted above. The metal-containing precursor(s) can initially be solid, liquid or gaseous material, provided that the metal precursor is in gas phase before it is conducted into the reaction chamber and contacted with the substrate surface. Pulsing a gaseous precursor onto the substrate means that the precursor gas is conducted into the chamber for a limited period of time. Typically, for single wafer processing, the pulsing time is from about 0.05 to 10 seconds. However, depending on the substrate type and its surface area, the pulsing time may be even higher than 10 seconds; in some cases from about 10 to about 60 seconds or more. For example, for batch reactors, pulse times may range from milliseconds to minutes or longer. For a 300 mm wafer in a single wafer reactor, the metal precursor can be pulsed from about 0.05 to about 10 seconds, from about 0.25 to about 3 seconds or from about 0.5 to about 2 seconds.

A second reactant in the cyclic deposition process can include an oxygen-containing reactant, to form metal or metal oxide particles or film on the substrate surface. An oxygen-containing reactant can be provided, for example, by pulsing diatomic oxygen gas or a mixture of oxygen and another gas, like ozone, into the reaction chamber.

In other embodiments, oxygen is formed inside the reactor, such as by decomposing oxygen containing chemicals. Oxygen containing chemicals that can be decomposed in the reactor to produce oxygen include, without limitation, H₂O, H₂O₂, N₂O, NO₂, O₃, and organic peroxides. Mixtures of such chemicals can also be used. In other embodiments, the catalytical formation of an oxygen containing pulse can be provided by introducing into the reactor a pulse of vaporized aqueous solution of H₂O₂ and conducting the pulse over a catalytic surface inside the reactor and thereafter into the reaction chamber. The catalytic surface is preferably a piece of platinum or palladium. In some embodiments, excited species of an oxygen-containing compound (e.g., oxygen cations, oxygen anions, oxygen radicals) may be used, which can be formed using an in-situ (or direct) or remote plasma (or radical) generator.

The second precursor can be pulsed from about 0.05 to about 10 seconds, from about 1 to about 5 seconds, or from about 2 to about 3 seconds. In some embodiments, the second precursor is pulsed from about 10 seconds to about 60 seconds, or even on the order of several minutes in some cases. In batch cyclic deposition (e.g., ALD) reactors, reactor volumes can be massive and therefore pulsing or purging of several minutes is not uncommon.

It will be appreciated that with each successive cycle, metal will be deposited over exposed substrate sections 602 and that cycles can be repeated as desired to achieve particles with desired particle size distributions, islands of catalytic material, or continuous or semi-continuous films.

In some cases, catalyst material 702 can be deposited as a continuous or non-continuous film and subsequently heated to form particles (e.g., nanoparticles) 902, illustrated in FIG. 9. The particles can form, for example, during step 112, described below. Alternatively, as noted above, the catalyst material can form particles/islands as the material is deposited. In this case, no further treatment of the catalyst may be required. In cases where deposited catalyst material 702 includes a metal oxide, catalyst material 702 can be exposed to a reducing environment (e.g., hydrogen gas and/or activated hydrogen gas) to form particles 902 or otherwise reduce the metal oxide.

After catalyst material 702, illustrated in FIGS. 7 and 8, is deposited onto exposed substrate sections 602, any remaining polymeric material (e.g., any remaining portions of second sections 502) can be removed during step 112. The polymeric material can be removed using an ashing, etch, solvent-based, or other suitable process. If catalyst material 702 or particles 902 are oxidized during this or another step, catalyst material 702 and/or particles 902 can be subjected to a reducing environment to reduce any oxides to metal.

During step 114, carbon nanotubes 1002, illustrated in FIG. 10, are formed using the catalyst material formed during step 110. Although illustrated as occurring after step 112, step 114 can alternatively be performed prior to step 112.

Suitable methods for growing carbon nanotubes during step 114 include decomposing a carbon-containing compound on the catalyst material (e.g., metal nanoparticle or nanocrystal sites) on the substrate surface. Typically, a carbon-containing compound, such as: methane, acetylene (C₂H₂), propylene, ethanol, or the like, is introduced to a reaction space along with a carrier gas, such as: hydrogen, nitrogen, or the like. Other hydrocarbons, such as heavier hydrocarbons like oils, can also be used. Typically, the carbon-containing compound disproportionates or decomposes at the catalytic site and the elemental carbon is incorporated into the structure of the carbon nanotubes.

Other methods of forming carbon nanotubes 1002 include using carbon monoxide (CO) as a carbon-containing compound along with a catalytic site, such as the metal islands or nanoparticles as described herein. Carrier gases such as hydrogen and nitrogen can be introduced into the reaction space along with the carbon monoxide. Water vapor and carbon dioxide can also be added to the reaction space to lower the carbon nanotube growth temperature and facilitate carbon nanotube growth.

Yet further techniques for forming films or particles or carbon nanotubes are disclosed in U.S. Pat. No. 7,491,634 entitled METHODS FOR FORMING ROUGHENED SURFACES AND APPLICATIONS THEREOF and in U.S. Pat. No. 8,545,936 entitled METHODS FOR FORMING CARBON NANOTUBES, the contents of which are hereby incorporated herein by reference, to the extent such contents do not conflict with the present disclosure.

Various devices can include nanotubes formed according to the methods described above. FIG. 11 illustrates an exemplary device 1100. Device 1100 includes a substrate 1102, a source 1110, a drain 1112, and one or more carbon nanotubes 1108 that form a channel between source 1110 and drain 1112. In the illustrated example, substrate 1102 includes base material 1104 and insulating material 1106 overlying base material 1104. Base material 1104 can include semiconducting material, such as silicon. Base material 1104 can serve as a back gate of the device. Alternatively, although not illustrated, a gate structure can be formed overlying carbon nanotube(s) 1108. Insulating material 1106 can include silicon oxide or other insulating or dielectric material. Source 1110 and drain 1112 can be formed of or include a suitable metal, such as silver, titanium, palladium, or aluminum.

Although exemplary embodiments of the present disclosure are set forth herein, it should be appreciated that the disclosure is not so limited. For example, although the structures, devices, and methods are described in connection with various specific chemistries, the disclosure is not necessarily limited to these examples. Further, although methods are illustrated in a particular sequence, the method is not limited to such sequence of steps, unless indicated herein to the contrary. Various modifications, variations, and enhancements of the devices, structures, and methods set forth herein may be made without departing from the spirit and scope of the present disclosure.

The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various processes, structures, devices, and configurations, and other features, functions, acts, and/or properties disclosed herein, as well as any and all equivalents thereof. 

What is claimed is:
 1. A method of forming carbon nanotubes on a surface of a substrate, the method comprising the steps of: providing a substrate in a reaction space, wherein the substrate comprises a surface and the surface comprises patterned polymeric material thereon and exposed substrate surface sections; using chemical vapor deposition, selectively form catalyst material only on the exposed substrate surface sections; and forming carbon nanotubes using the catalyst material.
 2. The method of claim 1, wherein said patterned polymeric material is formed using directed self-assembly polymeric material.
 3. The method of claim 1, further comprising a step of annealing polymeric material.
 4. The method of claim 1, wherein the patterned polymeric material is formed using a polymeric material comprising a block copolymer.
 5. The method of claim 4, wherein the method comprises a step of selectively removing a polymer of the block copolymer.
 6. The method of claim 1, wherein the patterned polymeric material is formed of a polymeric material initially comprising polystyrene (PS).
 7. The method of claim 1, wherein the patterned polymeric material is formed of a polymeric material initially comprising poly(methyl methacrylate) (PMMA).
 8. The method of claim 1, wherein the catalyst material comprises one or more of Cr, Cu, Ni, Fe, Co, Zn, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Mo and W.
 9. The method of claim 8, wherein said step of selectively forming catalyst material on the exposed substrate surface sections comprises selective decomposition of one or more organometallic compounds.
 10. The method of claim 1, wherein the exposed substrate surface sections comprise an insulating material.
 11. The method of claim 1, wherein the step of selectively forming catalyst material comprises atomic layer deposition.
 12. A method of forming carbon nanotubes on a surface of a substrate, the method comprising the steps of: providing a substrate having a surface; disposing a polymeric material onto the surface; annealing the polymeric material to form aligned phases of the polymeric material; removing portions of the polymeric material to form exposed substrate sections corresponding to the aligned phases; using chemical vapor deposition, selectively form catalyst material only on the exposed substrate sections; and forming carbon nanotubes using the catalyst material.
 13. The method of claim 12, wherein said polymeric material comprises a block copolymer.
 14. The method of claim 13, wherein the step of selectively forming catalyst material comprises selective decomposition of one or more organometallic precursors comprising the catalyst material.
 15. The method of claim 12, further comprising a step of forming features on the substrate surface prior to the step of disposing.
 16. The method of claim 12, further comprising a step of removing polymeric material after the step of selectively depositing catalyst material. 